U.S. patent number 7,038,889 [Application Number 10/260,971] was granted by the patent office on 2006-05-02 for method and apparatus for enhanced dual spin valve giant magnetoresistance effects having second spin valve self-pinned composite layer.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to James Mac Freitag, Hardayal Singh Gill, Mustafa Pinarbasi.
United States Patent |
7,038,889 |
Freitag , et al. |
May 2, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Method and apparatus for enhanced dual spin valve giant
magnetoresistance effects having second spin valve self-pinned
composite layer
Abstract
A dual spin valve giant magnetoresistance (GMR) sensor having
two spin valves with the second spin valve being self-biased is
disclosed herein. According to the present invention a dual spin
valve system is disclosed wherein the first of the two spin valves
in the dual spin valve element is pinned through exchange coupling,
i.e., a first anti-ferromagnetic pinning layer and a first
ferromagnetic pinned layer structure are exchange coupled for
pinning the first magnetic moment of the first ferromagnetic pinned
layer structure in a first direction. The second of the two spin
valves in the dual spin valve system is self-pinned. The
self-pinned spin valve does not use any anti-ferromagnetic layers
to pin the magnetization of the pinned layers.
Inventors: |
Freitag; James Mac (San Jose,
CA), Gill; Hardayal Singh (Palo Alto, CA), Pinarbasi;
Mustafa (Morgan Hill, CA) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
32029840 |
Appl.
No.: |
10/260,971 |
Filed: |
September 30, 2002 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20040061977 A1 |
Apr 1, 2004 |
|
Current U.S.
Class: |
360/314;
G9B/5.131; G9B/5.116; G9B/5.114; G9B/5; 360/324.12; 360/324.11;
257/E43.004 |
Current CPC
Class: |
B82Y
10/00 (20130101); B82Y 25/00 (20130101); G01R
33/093 (20130101); G11B 5/3954 (20130101); G11B
5/3903 (20130101); G11B 5/00 (20130101); G11B
5/313 (20130101) |
Current International
Class: |
G11B
5/39 (20060101) |
Field of
Search: |
;360/314,324.11,324.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Zhu, J.G. "Spin Valve and Dual Spin Valve Heads with Synthetic
Antiferromagnets," IEEE Transactions on Magnetics, vol. 35, No. 2,
Mar. 1999, pp. 655-660. cited by other .
Zhu, J.G. et al. "Micromagnetics of Dual Spin Valve GMR Heads," J.
Appl. Physics, vol. 79, No. 8, Part 2B, Apr. 1996, pp. 5886-5888.
cited by other .
Gill, "Dual Spin Valve Sensor Without AFM Pinning," U.S. Appl. No.
09/813,609 filed Mar. 20, 2001. cited by other.
|
Primary Examiner: Renner; Craig A.
Attorney, Agent or Firm: Chambliss, Bahner & Stophel,
P.C. Lynch; David W.
Claims
What is claimed is:
1. A method for forming a dual spin valve sensor having increased
sensitivity, comprising forming a first composite pinned layer, the
first composite pinned layer being exchange coupled via an
anti-ferromagnetic layer; forming a second composite pinned layer,
the second composite pinned layer being self pinned to eliminate a
need for an anti-ferromagnetic layer to reduce a thickness of the
dual spin valve sensor, wherein the second composite pinned layer
comprises at least first and second anti-parallel coupled self
pinned sub-layers; and forming a composite free layer disposed
between the first and second composite pinned layers.
2. The method of claim 1 wherein the composite free layer comprises
outer free layers with moments perpendicular to moments of the
first and second composite pinned layers.
3. The method of claim 1, wherein pinning of the moment of the
second composite pinned layer is reinforced through
magnetostriction to provide stable pinning of the moment.
4. The method of claim 1, wherein pinning of the moment of the
second composite pinned layer is reinforced to provide stable
pinning of the moment upon the application of a sense current
flowing through the composite free layer.
5. The method of claim 1, wherein the anti-ferromagnetic layer is
selected from the group consisting of PtMn, IrMn, FeMn and NiMn,
the anti-ferromagnetic layer providing strong exchange coupling
with the first composite pinned layer.
6. The method of claim 1, wherein the first composite pinned layer
comprises layers of CoFe/Ru/CoFe, wherein the CoFe layer nearer the
composite free layer is thicker than the CoFe layer farther away
from the composite free layer to provide signal addition for
increased sensitivity.
7. The method of claim 1, wherein the second composite pinned layer
comprises a first, a second layer, and a third layer, wherein the
first layer is thicker than the second layer and the third layer,
and wherein the first layer is nearer the composite free layer than
the second layer and the third layer to provide signal addition for
increased sensitivity.
8. The method of claim 1, wherein the second composite pinned layer
comprises layers of CoFe/Ru/NiFe, wherein the CoFe layer is thicker
than the NiFe layer, and wherein the CoFe layer is nearer the
composite free layer than the NiFe layer to provide signal addition
for increased sensitivity.
9. The method of claim 1, wherein the second composite pinned layer
comprises layers of CoFe/NiFe, wherein the CoFe layer is thicker
than the NiFe layer, and wherein the CoFe layer is nearer the
composite free layer than the NiFe layer to provide signal addition
for increased sensitivity.
10. The method of claim 1, wherein the second composite pinned
layer comprises layers of CoFeO/Ru/NiFeO, wherein the CoFeO layer
is thicker than the NiFeO layer, and wherein the CoFeO layer is
nearer the composite free layer than the NiFeO layer to provide
signal addition for increased sensitivity.
11. The method of claim 1, wherein the second composite pinned
layer comprises layers of CoFeO/NiFeO, wherein the CoFeO layer is
thicker than the NiFeO layer, and wherein the CoFeO layer is nearer
the composite free layer than the NiFeO layer to provide signal
addition for increased sensitivity.
12. The method of claim 1, wherein the second composite pinned
layer comprises layers of CoFe/Ru/CoFeNb, wherein the CoFe layer is
nearer the composite free layer than the CoFeNb layer for providing
increased sensitivity.
13. The method of claim 1, wherein the second composite pinned
layer comprises layers of CoFe/CoFeNb, and wherein the CoFe layer
is nearer the composite free layer than the CoFeNb layer for
providing increased sensitivity.
14. The method of claim 1, wherein the composite free layer
comprises layers of CoFe/NiFe/CoFe to provide increased sense
current flow.
15. A dual spin valve sensor comprising: an anti-ferromagnetic
layer; a first composite pinned layer being exchange coupled via
the anti-ferromagnetic layer; a second composite pinned layer, the
second composite pinned layer being self pinned to eliminate a need
for an anti-ferromagnetic layer to reduce a thickness of the dual
spin valve sensor, wherein the second composite pinned layer
comprises at least first and second anti-parallel coupled self
pinned sub-layers; and a composite free layer disposed between the
first and second composite pinned layers.
16. The sensor of claim 15 wherein the composite free layer
comprises outer free layers with moments perpendicular to moments
of the first and second composite pinned layers.
17. The sensor of claim 15, wherein a moment of the second
composite pinned layer is reinforced through magnetostriction to
provide stable pinning of the moment.
18. The sensor of claim 15, wherein a moment of the second
composite pinned layer is reinforced to provide stable pinning of
the moment upon the application of a sense current flowing through
the composite free layer.
19. The sensor of claim 15, wherein the anti-ferromagnetic layer is
selected from the group consisting of PtMn, IrMn, FeMn and NiMn,
the anti-ferromagnetic layer providing strong exchange coupling
with the first composite pinned layer.
20. The sensor of claim 15, wherein a first layer of the second
composite pinned layer is thicker than a second layer and a third
layer, and wherein the first layer is nearer the composite free
layer than the second layer and the third layer to provide signal
addition for increased sensitivity.
21. The sensor of claim 15, wherein the first composite pinned
layer comprises layers of CoFe/Ru/CoFe, wherein the CoFe layer
nearer the composite free layer is thicker than the CoFe layer
farther away from the composite free layer to provide signal
addition for increased sensitivity.
22. The sensor of claim 15, wherein the second composite pinned
layer comprises layers of CoFe/Ru/NiFe, wherein the CoFe layer is
thicker than the NiFe layer, and wherein the CoFe layer is nearer
the composite free layer than the NiFe layer to provide signal
addition for increased sensitivity.
23. The sensor of claim 15, wherein the second composite pinned
layer comprises layers of CoFe/NiFe, wherein the CoFe layer is
thicker than the NiFe layer, and wherein the CoFe layer is nearer
the composite free layer than the NiFe layer to provide signal
addition for increased sensitivity.
24. The sensor of claim 15, wherein the second composite pinned
layer comprises layers of CoFeO/Ru/NiFeO, wherein the CoFeO layer
is thicker than the NiFeO layer, and wherein the CoFeO layer is
nearer the composite free layer than the NiFeO layer to provide
signal addition for increased sensitivity.
25. The sensor of claim 15, wherein the second composite pinned
layer comprises layers of CoFeO/NiFeO, wherein the CoFeO layer is
thicker than the NiFeO layer, and wherein the CoFeO layer is nearer
the composite free layer than the NiFeO layer to provide signal
addition for increased sensitivity.
26. The sensor of claim 15, wherein the second composite pinned
layer comprises layers of CoFe/Ru/CoFeNb, wherein the CoFe layer is
nearer the composite free layer than the CoFeNb layer for providing
increased sensitivity.
27. The sensor of claim 15, wherein the second composite pinned
layer comprises layers of CoFe/CoFeNb, and wherein the CoFe layer
is nearer the composite free layer than the CoFeNb layer for
providing increased sensitivity.
28. The sensor of claim 15, wherein the composite free layer
comprises layers of CoFe/NiFe/CoFe to provide increased sense
current flow and increased sensitivity.
29. A magnetic storage system, comprising: a magnetic recording
medium; and a dual spin valve sensor operatively coupled proximate
the recording medium, the dual spin valve sensor, comprising an
anti-ferromagnetic layer; a first composite pinned layer being
exchange coupled via the anti-ferromagnetic layer; a second
composite pinned layer, the second composite pinned layer being
self pinned to eliminate a need for an anti-ferromagnetic layer to
reduce a thickness of the dual spin valve sensor wherein the second
composite pinned layer comprises at least first and second
anti-parallel coupled self pinned sub-layers--has; and a composite
free layer disposed between the first and second composite pinned
layers.
30. The system of claim 29 wherein the composite free layer
comprises outer free layers with moments perpendicular to moments
of the first and second composite pinned layers.
31. The system of claim 29, wherein the second composite pinned
layer comprises a moment, the moment of the second composite pinned
layer is reinforced through magnetostriction to provide stable
pinning of the moment.
32. The system of claim 29, wherein the second composite pinned
layer comprises a moment, the moment of the second composite pinned
layer is reinforced to provide stable pinning of the moment upon
the application of a sense current flowing through the composite
free layer.
33. The system of claim 29, wherein the anti-ferromagnetic layer is
selected from the group consisting of PtMn, FeMn, FeMn and NiMn,
the anti-ferromagnetic layer provides strong exchange coupling with
the first composite pinned layer.
34. The system of claim 29, wherein a first layer of the second
composite pinned layer is thicker than a second layer and a third
layer and wherein the first layer is nearer the composite free
layer than the second layer and a third layer to provide signal
addition for increased sensitivity.
35. The system of claim 29, wherein the composite free layer
comprises layers of CoFe/NiFe/CoFe to provide increased sense
current flow and increased sensitivity.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to dual spin valve heads for
magnetic storage systems, and more particularly to a method and
apparatus for enhanced dual spin valve giant magnetoresistance
(GMR) effects using two spin valves with the second spin valve
having a self-pinned composite layer.
2. Description of Related Art
The size and complexity of operating systems, user applications and
data files continues to increase. As a result, the importance of
magnetic storage systems is also increasing. To increase storage
capacity, the performance of magnetic heads is one focus of much
research. Magnetic heads are used for writing and reading data on
magnetic recording media. Anisotropic Magnetoresistive (AMR)
technology has been the primary, high performance read technology.
An AMR head employs a special conductive material that changes its
resistance in the presence of a magnetic field. As the head passes
over the surface of the disk, this material changes resistance as
the magnetic fields change corresponding to the stored patterns on
the disk. A sensor is used to detect these changes in resistance,
which allows the bits on the platter to be read.
However, even AMR heads have a limit in terms of how much areal
density they can handle. Successive generations of AMR heads were
reduced in size to allow still greater areal density. Sometimes
these more advanced designs were dubbed MRX for Extended
Magnetoresistive heads. However, giant magnetoresistive (GMR) heads
is the current focus in the logical progression of the storage
industry's endless quest for a way to increase areal density while
reducing the price per megabyte.
A typical GMR head design consists of a thin film inductive write
element and a read element. The read element consists of an GMR
sensor between two magnetic shields. The magnetic shields greatly
reduce unwanted magnetic fields coming from the disk; the GMR
sensor essentially "sees" only the magnetic field from the recorded
data bit to be read. In a merged head the second magnetic shield
also functions as one pole of the inductive write head. The
advantage of separate read and write elements is both elements can
be individually optimized. A merged head has additional advantages.
This head is less expensive to produce, because it requires fewer
process steps; and, it performs better in a drive, because the
distance between the read and write elements is less.
During operation, the inductive write head records bits of
information by magnetizing tiny regions along concentric tracks on
a disk. During reading, the presence of a magnetic transition or
flux reversal between bits causes the magnetic orientation in the
GMR sensor to change. This in turn, causes the resistance of this
sensor to change. The sensor's output voltage or signal is the
product of this resistance change and the read bias current. This
signal is amplified by low-noise electronics and sent to the HDD's
data detection electronics.
GMR sensors are composed of multiple thin films. GMR sensors have a
sensing layer, which responds to external magnetic fields. GMR
sensors include two magnetic layers separated by a spacer layer
chosen to ensure that the coupling between magnetic layers was
weak, unlike previously made structures. The magnetic orientation
of one of the magnetic layers is also "pinned" in one direction by
adding a fourth strong anti-ferromagnetic layer. In this
arrangement, the anti-ferromagnetic layer biases one of the
magnetic layers. Alternatively, a self-pinned magnetic layer may be
used. A self-pinned layer has a magnetic moment which is pinned
parallel to the magnetic moment by sense current fields from the
conductive layers.
The key structure is a spacer layer of a non-magnetic metal between
two magnetic metals. Magnetic materials tend to align themselves in
the same direction. So if the spacer layer is thin enough, changing
the orientation of one of the magnetic layers can cause the next
one to align itself in the same direction. During operation, the
magnetic alignment of the magnetic layers swing back and forth from
being aligned in the same magnetic direction (parallel alignment)
to being aligned in opposite magnetic directions (anti-parallel
alignment). The overall resistance is relatively low when the
layers are in parallel alignment and relatively high when in
anti-parallel alignment. When a weak magnetic field, such as that
from a bit on a hard disk, passes beneath such a structure, the
magnetic orientation of the unpinned magnetic layer rotates
relative to that of the pinned layer, generating a significant
change in electrical resistance due to the GMR effect.
A dual spin valve arrangement may also be used. With this
arrangement, the magnetoresistive coefficient is increased due to
the spin valve effect on each side of the free layer. The dual spin
valve sensor typically includes a five layer GMR film. The five
layer GMR film includes three ferromagnetic layers separated by two
thin conductive metallic layers. The two outer ferromagnetic layers
are generally exchange coupled. The pinned layer may have its
magnetization pinned by exchange coupling with an
anti-ferromagnetic (e.g., NiO or FeMn) layer. Alternatively, a
sense current may be used as the means for pinning the pinned layer
magnetization as opposed to the use of the conventional
anti-ferromagnetic layer.
However, each arrangement has its problems. Sensors formed with two
exchange coupled spin valves are too thick due to the presence of
thick anti-ferromagnetic pinning layers. This thickness is a
disadvantage that severely limits the sensitivity of these sensors
to minute changes in the magnetic flux. Still, this dual exchange
coupled spin valve sensor has at least one advantage, one being
that the magnetic moment pinned through exchange coupling is
strongly pinned thereby causing the free layer in the exchange
coupled spin valve system to exhibit stable biasing. The result is
a reliable, albeit, poorly sensitive, sensor.
The dual spin valve arrangement wherein the dual spin valve sensor
is formed with two self pinned spin valves do not require an
adjacent anti-ferromagnetic layer to pin the magnetic moment.
Advantageously, this type of dual spin valve sensor can be
fabricated thinner than the dual exchange coupled spin valve which
would lead to a more sensitive sensor. However, the dual self
pinned spin valve sensor lacks the stable biasing of the dual
exchange coupled spin valve sensor. The result is a sensitive, but
unreliable and unstable sensor.
It can be seen that there is a need for a method and apparatus for
providing enhanced giant magnetoresistance (GMR) effects to provide
increased sensitivity to minute changes in resistance in response
to magnetic flux interactions.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and
to overcome other limitations that will become apparent upon
reading and understanding the present specification, the present
invention discloses a method and apparatus for enhanced dual spin
valve giant magnetoresistance (GMR) effects using two spin valves
with the second spin valve being a self-pinned composite layer.
The present invention solves the above described problems via
development of a dual spin valve GMR sensor having the second of
two spin valves having a self-pinned composite layer that
significantly enhances sensing capabilities, refines sensitivity to
magnetic flux changes and provides more stable free layer
biasing.
Additional advantages result from the sensor being formed with a
thinner sensor stack than prior art sensors through the elimination
of an anti-ferromagnetic pinning layer. Enhanced sensitivity of the
sensor is demonstrated by improved sensitivity (.DELTA.R/R) and
increased sheet resistance. Desirable stable free layer biasing is
accomplished through implementation of a single exchange coupled
composite pinned layer in the dual spin valve sensor of the present
invention.
A method in accordance with the principles of the present invention
includes forming a first composite pinned layer, the first
composite pinned layer being exchange coupled via an
anti-ferromagnetic layer, forming a second composite pinned layer,
the second composite pinned layer being self pinned to eliminate a
need for an anti-ferromagnetic layer to reduce a thickness of the
dual spin valve sensor and forming a composite free layer disposed
between the first and second composite pinned layers.
In another embodiment of the present invention, a dual spin valve
sensor is provided. The dual spin valve sensor includes an
antiferromagnetic layer, a first composite pinned layer being
exchange coupled via the anti-ferromagnetic layer, a second
composite pinned layer, the second composite pinned layer being
self pinned to eliminate a need for an anti-ferromagnetic layer to
reduce a thickness of the dual spin valve sensor and a composite
free layer disposed between the first and second composite pinned
layers.
In another embodiment of the present invention, a magnetic storage
system is provided. The magnetic storage system includes a magnetic
recording medium and a dual spin valve sensor operatively coupled
proximate the recording medium, the dual spin valve sensor,
including an antiferromagnetic layer, a first composite pinned
layer being exchange coupled via the anti-ferromagnetic layer, a
second composite pinned layer, the second composite pinned layer
being self pinned to eliminate a need for an anti-ferromagnetic
layer to reduce a thickness of the dual spin valve sensor and a
composite free layer disposed between the first and second
composite pinned layers.
These and various other advantages and features of novelty which
characterize the invention are pointed out with particularity in
the claims annexed hereto and form a part hereof. However, for a
better understanding of the invention, its advantages, and the
objects obtained by its use, reference should be made to the
drawings which form a further part hereof, and to accompanying
descriptive matter, in which there are illustrated and described
specific examples of an apparatus in accordance with the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings in which like reference numbers
represent corresponding parts throughout:
FIG. 1 illustrates a storage system according to the present
invention;
FIG. 2 illustrates one particular embodiment of a storage system
according to the present invention;
FIG. 3 illustrates a slider mounted on a suspension;
FIG. 4 is an ABS view of the slider and the magnetic head;
FIG. 5 is a cross sectional view of a known dual spin valve sensor
having both magnetic moments being anti-ferromagnetic pinned;
FIG. 6 is a cross sectional view of a known dual spin valve having
both magnetic moments being self pinned;
FIG. 7 is a cross sectional view illustrating an embodiment of a
dual spin valve sensor according to the present invention;
FIG. 8 illustrates cross sectional view of a dual spin valve
element according to the invention showing the orientation of the
pinned magnetic moments and the direction of the sense current
cooperating to form the flux closure; and
FIG. 9 illustrates a side cross sectional view of a dual spin valve
element according to the invention showing the orientation of the
pinned magnetic moments and the direction of the sense current
cooperating to form the flux closure.
DETAILED DESCRIPTION OF THE INVENTION
In the following description of the exemplary embodiment, reference
is made to the accompanying drawings which form a part hereof, and
in which is shown by way of illustration the specific embodiments
in which the invention may be practiced. It is to be understood
that other embodiments may be utilized as structural changes may be
made without departing from the scope of the present invention.
The present invention solves the above-described problems by
forming a GMR sensor including dual spin valves being formed of
composite thin film layers and having a composite thin film free
layer sandwiched between the two spin valves, wherein the first of
two spin valves in the dual spin valve element is pinned through
exchange coupling and the second of two spin valves in the dual
spin valve system is self pinned and does not use any
anti-ferromagnetic layers to pin the magnetization of the pinned
layers. The first and second composite pinned layers have first and
second magnetic moments, respectively, wherein the first and second
magnetic moments are parallel.
FIG. 1 illustrates a storage system 100 according to the present
invention. In FIG. 1, a transducer 110 is under control of an
actuator 120. The actuator 120 controls the position of the
transducer 110. The transducer 110 writes and reads data on
magnetic media 130. The read/write signals are passed to a data
channel 140. A signal processor 150 controls the actuator 120 and
processes the signals of the data channel 140. In addition, a media
translator 160 is controlled by the signal processor 150 to cause
the magnetic media 130 to move relative to the transducer 110. The
present invention is not meant to be limited to a particular type
of storage system 100 or to the type of media 130 used in the
storage system 100.
FIG. 2 illustrates one particular embodiment of a storage system
200 according to the present invention. In FIG. 2, a hard disk
drive storage system 200 is shown. The system 200 includes a
spindle 210 that supports and rotates a magnetic disk 214. The
spindle 210 is rotated by a motor 228 that is controlled by a motor
controller 230. A combined read and write magnetic head 240 is
mounted on a slider 242 that is supported by a suspension 244 and
actuator arm 246. Processing circuitry 250 exchanges signals,
representing information, with the head 240, provides drive signals
to the motor 228 for rotating the magnetic disk 214, and provides
control signals to the actuator motor 260 for moving the slider 242
to various tracks. A plurality of disks 214, sliders 242 and
suspensions 244 may be employed in a large capacity direct access
storage device.
The suspension 244 and actuator arm 246 position the slider 242 so
that the magnetic head 240 is in a transducing relationship with a
surface of the magnetic disk 214. When the disk 214 is rotated by
the motor 228, the slider 240 is supported on a thin cushion of air
(air bearing) between the surface of the disk 214 and the
air-bearing surface (ABS) 248. The magnetic head 240 may then be
employed for writing information to multiple circular tracks on the
surface of the disk 214, as well as for reading information
therefrom.
FIG. 3 illustrates a slider 310 mounted on a suspension 312. In
FIG. 3 first and second solder connections 304 and 306 connect
leads from a GMR sensor 308 to leads 313 and 314 on the suspension
312 and third and fourth solder connections 316 and 318 connect the
coil 384 to leads 324 and 326 on the suspension.
FIG. 4 is an ABS view of the slider 400 and the magnetic head 404.
The slider has a center rail 456 that supports the magnetic head
404, and side rails 458 and 460. The rails 456, 458 and 460 extend
from a cross rail 462. With respect to rotation of a magnetic disk,
the cross rail 462 is at a leading edge 464 of the slider and the
magnetic head 404 is at a trailing edge 466 of the slider.
The above description of a typical magnetic recording disk drive
system, shown in the accompanying FIGS. 1 4, are for presentation
purposes only. Disk drives may contain a large number of disks and
actuators, and each actuator may support a number of sliders. In
addition, instead of an air-bearing slider, the head carrier may be
one which maintains the head in contact or near contact with the
disk, such as in liquid bearing and other contact and near-contact
recording disk drives. Further, the ABS of the slider may be
different from that shown in FIG. 4 and the location of the head is
not meant to be limited to that shown in FIGS. 3 4.
FIG. 5 shows an air bearing surface (ABS) view of a prior art dual
spin valve sensor 500 having magnetic moments that are
anti-ferromagnetically pinned. The dual spin valve sensor 500 has
end regions 502 and 504 separated from each other by a central
region. The central region has defined edges where the end regions
502 and 504 form a contiguous junction with and abut the edges. The
end regions 502 and 504 forming leads which are formed over hard
biased layers 503 and 505, respectively. The leads formed in ends
502 and 504 of dual spin valve sensor 500 provide electrical
connection between the dual spin valve sensor 500 and a sense
current source 536 and a sensing means 538. The sense current
source 536 provides the necessary sense current Is to the dual spin
valve sensor element 599 to establish a DC base (bias) voltage
across the dual spin valve sensor element 599. The sensing means
538 provides the means for sensing the spin valve effect.
Thin film stacks, which make up spin valve sensors, are grown on a
substrate (not shown in the Figs.). Usually, a starter or seed
layer (not shown) is initially grown on the substrate, and all
additional layers are grown thereon.
The first layer of the prior art dual spin valve sensor is an
anti-ferromagnetic pinning layer 514. Disposed upon the
anti-ferromagnetic pinning layer 514 is a first composite
ferromagnetic pinned layer 516. Elements including the composite
layer of the prior art composite ferromagnetic pinned layer are
CoFe 551, Ru 552 and CoFe 553.
Disposed on the first ferromagnetic composite pinned layer 516 is a
first nonmagnetic electrically conductive spacer layer 518.
Disposed on the first nonmagnetic electrically conducting spacer
layer 518 is a composite ferromagnetic free layer 520. The
composite ferromagnetic free layer 520 includes a composite layer
of CoFe 561, NiFe 562 and CoFe 563.
Disposed on the composite ferromagnetic free layer 520 is a second
nonmagnetic electrically conducting spacer layer 522. Disposed upon
the second nonmagnetic electrically conducting spacer layer 522 is
a second composite ferromagnetic pinned layer 524. Elements
including the composite layer of the second composite ferromagnetic
pinned layer are CoFe 571, Ru 572 and CoFe 573.
Disposed upon the second composite ferromagnetic pinned layer 524
is a second anti-ferromagnetic pinning layer 525. A cap layer 526
is disposed upon the second anti-ferromagnetic pinning layer
525.
Now, regarding FIG. 5, the first composite ferromagnetic pinned
layer 516 is disposed adjacent the first anti-ferromagnetic pinning
layer 514 and the second ferromagnetic pinned layer 524 is disposed
adjacent the second anti-ferromagnetic pinning layer 525. The
pinned layers 516, 524 are pinned through exchange coupling with
their respective anti-ferromagnetic pinning layers 514 and 525.
Prior art dual spin valve sensors having two anti-ferromagnetically
pinned spin valves, as shown in FIG. 5, are disadvantaged because
of the great size of the dual spin valve element 599. The
anti-ferromagnetic layers (514 and 525) are on the order of a
hundred angstroms thick, and often more. Due to the great size of
these GMR elements, the sheet resistance is low, thus the
sensitivity is low. As sensor sensitivity increases, smaller and
smaller magnetic flux interactions are detectable, thus allowing
more and more data to be stored on magnetic media. Thus, high
sensitivity and sheet resistance are highly desirable.
FIG. 6 shows an air bearing surface (ABS) view of a prior art dual
spin valve sensor 600 where the magnetic moments of both spin
valves are self pinned. The external structure of the dual spin
valve sensor 600 bounding the dual spin valve element 699 may be
identical to that disclosed in FIG. 5 and will not be repeated.
The first layer of the prior art dual spin valve sensor according
to FIG. 6, is a first self pinned composite layer 616. The first
self pinned composite layer 616 is a composite layer including
layers of NiFe 651, Ru 652 and NiFe 653. Disposed on the first self
pinned composite layer 616 is a first nonmagnetic electrically
conductive spacer layer 618.
Disposed on the first nonmagnetic electrically conducting spacer
layer 618 is a free layer 620 including NiFe. Disposed on the free
layer 620 is a second nonmagnetic electrically conducting spacer
layer 622. Disposed upon the second nonmagnetic electrically
conducting spacer layer 622 is a second self pinned layer 624
including NiFe.
Disposed upon the second self pinned layer 624 is a cap layer 626
disposed as the top layer of the dual spin valve element 699.
Reference numbers not specifically identified in FIG. 6 correspond
to those reference numbers previously defined in subsequent
Figs.
Referring to FIG. 6, prior art dual spin valve sensors having two
self pinned spin valves 600, such the one shown in FIG. 6, are
disadvantaged because of the instability of the biasing for the
dual spin valve element 699. The self pinned layers 616, 624 are
highly susceptible to demagnetizing fields. The pinning field can
be reversed in the presence of the sense current induced magnetic
field or other magnetic fields which may interact with the self
pinned fields.
The present invention provides increased magnetic field sensitivity
by combining a sensitive self pinned spin valve with a strong
biasing anti-ferromagnetic spin valve, i.e., the dual spin valve
sensor of the present invention provides increased .DELTA.R/R and
high sensitivity while maintaining stable biasing in the presence
of induced magnetic fields.
Now, with reference to FIG. 7, an air bearing surface (ABS) view of
an asymmetric dual spin valve sensor 700, according to another
embodiment of the present invention, is disclosed. The external
structure of the dual spin valve sensor bounding the dual spin
valve element 799 may be identical to that disclosed in FIG. 5 and
will not be repeated.
The structures of composite layers 716, 720 and 724 will now be
disclosed. The exchange coupling pinned layer 716 is a composite
layer including CoFe 751, Ru 752 and CoFe 753. The layer of CoFe
751 has a magnetic moment 758 oriented out of the page, as shown in
FIG. 7, due to exchange coupling with anti-ferromagnetic layer 714.
The layer Ru 752 (an anti-parallel coupling layer) cooperates with
layer CoFe 753 causing anti-parallel coupling of the magnetic
moments (758 and 759, respectively) of layers CoFe 751 and CoFe
753.
The composite free layer 720 includes CoFe 761, NiFe 762 and CoFe
763. In the properly biased condition, layer CoFe 761 and CoFe 763
having magnetic moments 768 and 769, respectively, perpendicular to
the magnetic moments of the pinned layers.
The self-pinned layer 724 is a composite layer including CoFe 771,
Ru 772 and NiFe 773. The layer of CoFe 771 has a magnetic moment
778 oriented into of the page, as shown in FIG. 7. The layer Ru 772
(an anti-parallel coupling layer) cooperates with layer NiFe 773
causing anti-parallel coupling of the magnetic moments (778 and
779, respectively) of layers CoFe 771 and NiFe 773.
The magnetic moments 778 and 779 are self pinned through the sense
current and magnetostriction, and the additional contribution of an
added antiparallel coupling layer 772. The anti-parallel coupling
layer increases the magnetic anisotropy through anti-parallel
coupling the layers 771 and 773. The thickness of the respective
layers 771 and 773 also contributes to increasing the magnetic
anisotropy of the self pinned composite layer 724. The self pinned
composite layer does not have and does not require an adjacent
anti-ferromagnetic layer to cause pinning because the magnetic
moments of the self pinned layer are oriented at least due to the
sense current and magnetostriction.
Alternatively, the second ferromagnetic self pinned layer may be a
composite layer of CoFeO and NiFeO, instead of CoFe and NiFe.
Reference numbers not specifically identified in FIG. 7 correspond
to those reference numbers previously defined in subsequent
Figs.
The dual spin valve sensor 700 of the instant invention includes
two composite pin layers 716, 724. Sandwiched between the two
composite layers is the center composite free layer 720. Here it is
pointed out, with reference to FIG. 7, that the exchange coupling
pinned layer 716 is disposed on the first anti-ferromagnetic
pinning layer 714. The exchange coupling pinned layer is pinned
through exchange coupling with the first anti-ferromagnetic pinning
layer 714. The exchange coupling pinned layer has a net magnetic
moment oriented in accordance with the strength of the pinning
field.
The self-pinned layer 724 has a net magnetic moment oriented in
accordance with the induced fields from the applied sensing
current. The magnetic field associated with the self-pinned layer
724 also works cooperatively with the anti-ferromagnetically pinned
layer 716 to form a flux closure around the free layer structure
720 in the central sensing region.
FIG. 8 illustrates cross sectional view of a dual spin valve
element 800 according to the invention, which shows the orientation
of the pinned magnetic moments 858, 859, 878 and 879, (into and out
of the page, respectively) and the direction of the sense current
801 (left to right) cooperating to form a flux closure shown
generally surrounding the free layer 820. The magnetic field lines
(891 and 894), emanating from the sense current direction 801 act
constructively with the magnetic fields associated with pinned
magnetic moments 858, 859, 878 and 879. Reference numbers not
specifically identified in FIG. 8 correspond to those reference
numbers previously defined in subsequent Figs.
FIG. 9 illustrates a side cross sectional view of a dual spin valve
element 900 according to the invention, which shows the orientation
of the pinned magnetic moments 958, 959, 978 and 979, (pointing
from left to right and pointing from right to left) and the
direction of the sense current 901 (into the page) cooperating to
form the flux closure shown generally surrounding the free layer.
The magnetic field lines (991 and 994), emanating from the sensing
current 901 act constructively with the magnetic fields associated
with pinned magnetic moments 958, 959, 978 and 979 to form the flux
closure around the free layer in the sensing region. Reference
numbers not specifically identified in FIG. 9 correspond to those
reference numbers previously defined in subsequent Figs.
Referring to both FIGS. 8 and 9, magnetizations (magnetic moments,
858, 859, 878, 879, 958, 959, 978 and 979, respectively), are
oriented along prescribed directions. The magnetic moments (858,
859, 878, 879, 958, 959, 978 and 979, respectively) of the two
pinned layers (816 and 824, respectively) are aligned, and point in
same directions, i.e., they are parallel (symmetric).
The magnetic moments 858, 859, 878, 879, 958, 959, 978 and 979, of
the two pinned layers are oriented parallel to one another as
illustrated in FIGS. 8 and 9. The magnetic fields arising from the
parallel magnetic moments 858, 859, 878, 879, 958, 959, 978 and
979, reinforce each other at the central sensing region of the
ferromagnetic free layer structure (820) forming a flux guiding
area shown generally in FIGS. 8 and 9.
Allowing the sense current I.sub.s to flow along a direction 801,
901 such that the sense current I.sub.s reinforces flux guiding
shown generally in FIGS. 8 and 9 (the direction 801, 901 of the
sense current I.sub.s being aligned with and corresponding to the
direction of the magnetic field lines 891, 894, 991 and 994,
respectively, corresponding to the magnetic moments 858, 859, 878,
879, 958, 959, 978 and 979), causing the dual spin valve GMR sensor
to be self-biased, and the self biasing remains stable in the
presence of magnetic flux interactions.
In the symmetric (parallel) dual spin valve element of the present
invention (800 and 900, respectively), the free layer 820 is free
from demagnetizing fields arising from the pinned layers (816 and
824).
As illustrated in FIGS. 8 and 9, the magnetic moments (858, 859,
878, 879, 958, 959, 978 and 979, respectively) are assumed to have
opposite sign, but identical magnitude resulting in the dual spin
valve element (800 and 900) being self biased, i.e., the
demagnetizing fields arising from the pinned outer magnetic layers
816, 824 reinforce each other in the region of the free layer
820.
The magnetizations of the outer layers 816, 824 form a flux
enclosure or guide surrounding the free layer 820 shown generally
in FIG. 8. When the sense current I.sub.s in the free layer 820
flows in the direction such that it reinforces the flux enclosure
formed by the layers, rather than opposing it, the self biasing is
made stable and efficient.
The magnetic field induced by the sense current I.sub.s also
reinforces the pinning of the magnetic moment of the self pinned
layers, especially in cases where the sense current is large. Large
sense currents may produce induced magnetic fields several times
larger than the magnetic fields emanating from the pinned layers.
The result is a very stable biased free layer and a sensitive spin
valve sensor with large .DELTA.R/R.
The ferromagnetic free layer structure (720 and 820, respectively)
lies within the generally shown flux closure area and is free from
demagnetizing fields. A strong flux closure formed by the present
invention ensures a well biased sensor. Good biasing demonstrated
by the present invention causes significant increased sensitivity
to sensed magnetic flux interactions.
Further advantages are gained through arrangement and construction
of the second ferromagnetic self pinned layer (724 and 824,
respectively). The second ferromagnetic self-pinned layer (724 and
824, respectively) may be a composite layer including at least CoFe
or CoFeO (771) and NiFe, NiFeO or CoFeNb (773), and further,
wherein the CoFe or CoFeO layer is thicker than the NiFe, NiFeO or
CoFeNb layer. Having the CoFe or CoFeO layer thicker than the NiFe,
NiFeO or CoFeNb layer causes signal addition to take place, thus in
effect amplifying the magnetic flux signal sensed from the magnetic
media. An overall result of the construction of the self pinned
layer (724 and 824, respectively) described above is increased
.DELTA.R/R (sensitivity) of the dual spin valve sensor that allows
the sensor to detect more minute magnetic flux interactions which
allows magnetic media to be more densely packed with data.
The combination of a sensitive self pinned spin valve (724 and 824,
respectively) with an anti-ferromagnetic spin valve (716 and 816,
respectively), as disclosed herein, produces a dual spin valve
sensor with increased .DELTA.R/R featuring high sensitivity while
maintaining stable biasing in the presence of induced magnetic
fields.
The elimination of one exchange coupled layer by the present
invention, considerably reduces the overall thickness of dual spin
valve element, which results in increased sheet resistance, a
greater GMR ratio and increased sensitivity to detected magnetic
flux, over prior art sensors having two exchange coupled spin
valves, as shown in FIG. 5. The implementation of one exchange
coupled spin valve provides desired stable biasing of the free
layer, over prior art sensors having two self pinned spin valves,
as shown in FIG. 6. The implementation of one self pinned spin
valve provides improved sensitivity, over prior art sensors having
two exchange coupled spin valves, as shown in FIG. 5.
As mentioned above, the present invention provides a method and
apparatus for providing enhanced giant magnetoresistance (GMR)
effects by forming a GMR head including dual spin valves being
formed of composite thin film layers and having a composite thin
film free layer sandwiched between the spin valves, the second of
the two spin valves being self-pinned.
The foregoing description of the exemplary embodiment of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of the above teaching. It is
intended that the scope of the invention be limited not with this
detailed description, but rather by the claims appended hereto.
* * * * *